1. Field of the Invention
The present invention relates to display devices and methods of fabricating display devices. More particularly, the present invention relates to a color filter panel of a liquid crystal display (LCD) device and a method of fabricating the same using a color filter transfer film.
2. Discussion of the Related Art
Generally, flat panel display devices are thin, light in weight, consume low amounts of power and are, therefore, commonly used as displays for portable electronic devices. Because of their superior resolution and ability to produce high-quality color images, liquid crystal display (LCD) devices are commonly used in laptop computers and desktop computer monitors.
LCD devices generally include an LCD panel having upper and lower substrates supporting opposing electrodes that are spaced apart from each other by liquid crystal material. Active matrix LCDs (AM-LCDs) include thin film transistors (TFTs) and pixel electrodes arranged in a matrix pattern and display high resolution moving images. LCD devices can display desired images by applying voltages, which correspond to externally input image data, to the opposing electrodes. Upon receiving the applied voltages, electric fields are induced within the liquid crystal material. The induced electric field affects an alignment of molecules of the liquid crystal material. Given that liquid crystal molecules exhibit anisotropic optical properties, light transmissivity characteristics of the liquid crystal molecules changes when the alignment of the liquid crystal molecules is affected by an induced electric field. Accordingly, when electric fields are selectively induced within liquid crystal material, angles at which the liquid crystal material refracts incident light is selectively controlled to display an image.
As mentioned above, LCD devices generally include an LCD panel having an upper substrate and a lower substrate separated by a layer of liquid crystal material. The upper substrate (i.e., a color filter substrate) includes a common electrode and a color filter layer while the lower substrate (i.e., an array substrate) includes pixel electrodes and switching elements such as thin film transistors (TFT's).
The color filter layer generally includes red (R), green (G) and blue (B) color filters disposed in a predetermined filter pattern by known means such as pigment dispersion methods, inkjet methods, laser (thermal) transferring methods, or film transferring methods. The pigment dispersion method is capable of producing intricate color filter patterns yielding excellent color reproduction characteristics and is therefore widely used in forming color filter layers. Forming color filter layers by the pigment dispersion method, however, may become excessively complicated as it requires many process steps (e.g., color resist deposition, light exposure, resist development, resist curing, etc.).
To overcome the aforementioned problems inherent in the pigment dispersion method, thermal transferring methods have been proposed and developed for use in forming color filter layers. Briefly, in the related art thermal transferring method, a laser is used to selectively irradiate a color filter transfer film. FIG. 1 illustrates a cross sectional view of a related art color filter transfer film.
Referring to FIG. 1, a related art color filter transfer film 10 includes three layers: a base film 10a; a light-to-heat conversion (LTHC) layer 10b; and a color filter layer 10c. The base film 10a is formed of a transparent polymer having suitable light transmissivity properties (e.g., polyester or polyethylene) and supports the LTHC and color filter layers 10b and 10c, respectively. Accordingly, laser light can be efficiently transmitted through the base film 10a to the LTHC layer 10b. The LTHC layer 10b is formed of an organic chemical compound (e.g., carbon black or IR(infrared)-pigment), a metallic material (e.g., aluminum), an oxide metal, or a combination thereof) and converts incident light into thermal energy (i.e., heat). The color filter layer 10c is formed of a resin material having a single color pigmentation (e.g., red, green, or blue). During a thermal transferring process, portions of the color filter layer 10c are transferred onto a color filter substrate as illustrated with respect to FIGS. 2A to 2F.
Referring to FIG. 2A, an opaque layer (e.g., opaque metallic material or a black resin) is first formed on a surface of substrate 30 and is subsequently patterned via known photolithography processes to form a black matrix 35.
Referring to FIG. 2B, a first color filter transfer film 10 having a structure substantially as described above with respect to FIG. 1, and having a first color, is aligned over the surface of the substrate 30 supporting the black matrix 35. Next, the color filter transfer film 10 is pressed against the substrate 30 and black matrix 35.
Referring to FIG. 2C, a laser source 50, capable of generating a laser beam, is arranged over the color filter transfer film 10. Thereafter, the laser source 50 is repeatedly turned on and off while the laser source 50 and a substrate stage (not shown) move along predetermined directions, causing the laser source 50 to selectively irradiate predetermined portions of the color filter transfer film 10. Specifically, the laser source 50 is turned on whenever it passes over first regions (I) of the substrate 30 (i.e., where first color filters having a first color pigmentation are to be formed). The laser source 50 is turned off whenever it passes over the black matrix 35 and second and third regions (II) and (III) of the substrate 30, where the first color filters are not to be formed. Accordingly, only areas corresponding to the first regions (I) are irradiated with a laser beam from the laser source 50. While the laser source 50 is turned on, portions of the LTHC layer 10b arranged within the first regions (I) of the substrate 30 absorb the irradiated laser light and covert the irradiated light into heat. The heat converted by the LTHC layer 10b causes adjacent portions of the color filter layer 10c (i.e., portions of the color filter layer 10c arranged within the first regions (I) of the substrate 30), to become transferred onto the substrate 30.
Referring to FIG. 2D, after the laser source 30 irradiates the first regions (I) of the substrate 30, first color filter transfer film 10 is removed, causing first color filters 40 to remain within the first regions (I) on the substrate 30, between the black matrix 35.
Referring to FIG. 2E, second and third color filters 42 and 44, respectively, are sequentially formed on the substrate 30 in the same manner as the first color filter, illustrated in FIGS. 2B–2D. Thus, second color filters 42 are formed within second regions (II) of the substrate 30 and third color filters 44 are formed within third regions (III) of the substrate 30 such that the first, second, and third color filters 40, 42, and 44 are separated by the black matrix 35. By way of illustration, the first color filter 40 can contain red color pigmentation, and the second and third color filters 42 and 44 can contain green and blue color pigmentations, respectively.
Next, the substrate 30 is heated to a predetermined temperature to cure the resin material forming the newly formed first to third color filters 40, 42, and 44. Alternatively, a curing process can be performed after each of the first to third color filters 40, 42 and 44 are formed on the substrate 30. Curing the substrate 30 between formation of successive color filters is beneficial because it helps to prevent the resin material forming the color filters from intermixing.
Referring to FIG. 2F, an overcoat layer 46 is formed over the entire substrate 30, covering the color filters and the black matrix 35 after the first, second, and third color filters 40, 42 and 44, have been cured. The overcoat layer 46 protects the underlying color filters 40, 42 and 44 and eliminates step formations generated by the color filters, thereby planarizing the surface of the substrate 30. Next, a transparent common electrode 48 (e.g., formed of indium-tin-oxide (ITO) or indium-zinc-oxide (IZO)) is formed on the overcoat layer 46.
While generally successful, the related art thermal transferring method is not without its disadvantages. For example, the time required to form a complete color filter layer may be unduly long and complicated as red, green, and blue color filter transfer films each have to be separately pressed to the substrate 30, selectively irradiated by the laser source 50, and carefully removed from the substrate 30. Furthermore, defects such as micro bubbles, voids, impurities, etc., may be created between the substrate 30 and the various color filters because of the numerous color filter transfer films that must be repeatedly adhered to and removed from the substrate 30. Such defects may cause the various color filters to delaminate from the substrate 30. Moreover, since only predetermined regions of the color filter transfer film 10 are to be selectively irradiated, the related art thermal transferring method requires that the laser source be frequently turned on and off. Such cycling of the laser source may deleteriously form color filters with rough peripheral edges.